1. Field of the Invention
The invention relates to a continuous process for preparing polymers with silane end groups by polymer-analogous continuous reaction of reactive silane monomers with functionalized polymers.
2. Description of the Related Art
The change in the functionalization of oligomers and polymers by polymer-analogous reactions is an important process step in the chemical industry. As a result, it is possible to tailor the properties of polymers to the particular field of use. For example, the reactivity, the crosslinking characteristics, the adhesion, the solubility, the morphology, the thermal stability, etc., can be adjusted. Examples of polymer-analogous reactions are the hydrolysis of polyvinyl acetate to polyvinyl alcohol, the hydrosilylation of polysiloxanes bearing H groups with olefins, the quaternization of polyvinylpyridine. In addition, the functionalization of oligomers and polymers with reactive groups also constitutes an important reaction. Of particular interest here is also the incorporation of monomeric reactive silane groups. In many cases, for this purpose, functionalized polymers such as OH-, NH- or SH-containing polyethers, polyesters, polyurethanes or polysulfides are reacted with isocyanatosilanes, or else isocyanate-functional polymers are capped by simple reaction with aminosilanes.
For some of these polymer-analogous reactions, for example, hydrosilylation, continuous processes have already been described and performed in U.S. Pat. No. 6,350,824.
In this context, continuous processes are superior to batch processes in the following aspects:                uniform product quality, i.e. reduction in the side reactions, short thermal stress on starting materials and products, increased selectivity of the reaction;        high space-time yield, i.e. high quantitative output with simultaneously small reactor holdup, as a result superior to the batch process also in safety and toxicological aspects;        multistage reactions possible without backmixing, i.e. activation and deactivation take place in separate plant parts;        minimization of waste and production cost minimization as a result of minimization and/or absence of solvents in inhomogeneous systems;        mixing of highly viscous products is better in continuous mixers;        a further advantage of continuous processes is that in-line analysis allows the quality of the resulting product to be controlled during the running production process by adjusting reaction parameters such as residence time, temperature profiles, stoichiometry of the components used, etc. In addition, these processes can be optimized in a simpler manner and more efficient raw material use is thus possible.        
According to the prior art to date, the functionalization of polymers with isocyanatosilanes or aminosilanes is performed only in batch processes. Typical examples of these reactions are described in EP 931 800 B1, U.S. Pat. No. 5,068,304, DE 198 49 817 or WO 03/018658. None of the processes published to date discusses means of industrial realization and optimization in continuous processes. At the same time, it is common knowledge that, for example, in the preparation of polyurethanes and also silane-terminated polyurethanes, the control of the reaction conditions has an extremely important influence on the product quality. Moreover, in the scale-up of such processes, problems often occur in reproducibility, since, for example, the temperature control and the mixing of the reactants changes.
In the case of end termination with isocyanatosilanes, in addition to the variation in the polymer preparation, further side reactions are also possible which can lead to degradation of the isocyanatosilane, and hence often have the consequence of low functionalization of the polymer. Although these effects can be compensated for by a higher addition of silane, the amounts of the specialty silanes required is thus increased simultaneously, which is in many cases undesired for reasons of cost.